apple store declined purchase of a mac on split purchase between 2 bank cards

apple store declined purchase of split purchase between the apple card and bank card for one mac.

They claim that kind of purchase is not allowed on special order macs (e.g. 128GB Ram). They are allowed split payment if the Mac is already in stock.

I am expecting half the cost of the mac on the apple card at 0% apr which I already have the credit. The other half on my bank card.